Phonological Deficits in Aphasia

R. Sunil KumarR. Sunil Kumar

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Introduction

The sounds that make up words are organized in specific ways.

Some features of the organization of the sounds of the words are universal to all human languages.

Others are particular properties of individual languages.

Phonology is the description of the system and patterns of these sounds that occur in a language. 2

The description could be either phonetic or phonemic.

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Phonemes:

Phonemes are abstract representation of the sound segments relevant to the words of a language,

which are mapped in complex ways onto articulatory gestures and acoustic waveforms.

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Word production & perception

To produce a word, it requires access to the representation (phonological planning) and the conversion of such a representation into articulatory commands.

Conversely, to perceive a word, it requires converting a continuous acoustic signal into a discrete phonetic – phonological representation for lexical access.

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Disturbances in the production of sounds can be divided into those affecting the actual mechanism of articulation and those affecting the process of planning the sounds in a word.

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Blumstein (1973), studied particular types of errors in the spontaneous speech of 5 Broca’s, 6 Conduction aphasias and 6 Wernicke’s aphasics.

She found that all the three groups of patients did not differ with respect to total phonemic inventory skills.

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Phonemic Paraphasias

Phonemic paraphasias arise at a stage of sentence planning at which the sound of content words – but not the function words – is being planned.

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Phonemic paraphasias

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Garrett, 1982, suggested that the phonemic paraphasias arise due to deficits in the stage of processing of phonological representation at which the link between word meaning and word sound is utilized.

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According to Caplan, 1986, the disturbances of this sort only account for errors made in naming pictures and other tasks which involve deriving phonological forms from semantic representations and

cannot apply to any task in which there is a route from phonological representation of the input side directly to a phonological representation which is involved in speech planning.

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This means that there are two different types of disturbances involved in speech planning which can give rise to phonemic paraphasias.

They are1.Disturbance in accessing lexical

phonological representations,2.Disturbance in accessing superficial

phonological representations.

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Milberg et al, 1988, concluded that the impairments displayed by the aphasic patients may be due to the processing mechanisms contributing to lexical access.

There may be change in the threshold of sensitivity for activation of the lexicon.

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The fluent aphasics could be characterized by a decreased threshold of sensitivity of lexical access and thus

they would show a lessened sensitivity to phonological distortion, subsequently accessing more words in the lexicon than normal.

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In contrast, the nonfluent aphasics could be characterized as having an increased threshold of sensitivity to lexical access and thus

would show an increased sensitivity phonological distortion, subsequently accessing fewer words in the lexicon than normal.

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Comprehension deficits at phonological level

Alajouanine et al, 1964, tested a group of 19 individuals who made phonological errors in spontaneous speech.

They argued that the presence of phonemic paraphasia is always accompanied by a deficit in “the ability to use auditory sensory information”.

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Shattuck – Hufnagel, 1979, reported that speech errors, which are phonologically related to their targets, are produced in varying proportions by the majority of aphasic patients.

They can be either real words or non-words that are clearly related with the target word.

For example, test/chest and anymay/anyway are both errors produced in the spontaneous speech of aphasic subjects.

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Caramazza, 1983, reported an aphasic subject who showed deficits in auditory comprehension tasks, they also made phonological errors in production tasks.

They further stated that the written comprehension of the subject was intact.

Caramazza et al, accounted for this pattern in terms of phonological processing deficits that effect performance in all tasks requiring the generation of a phonological code.

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Allport (1985) asserted that there could be an association between phonological deficits in comprehension and production.

He suggested that the lexicon comprises a set of auto associated patterns within a phonological space and these patterns are the basis of both spoken word recognition and production.

He further argued that there is reduced discrimination of many or all learned patterns, necessarily affecting the retrieval of these word forms for both input and output.

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Dell (1985, 89) suggested that the interactive activation lexical network, which accounts for patterns of speech errors in production, is also used for lexical access in comprehension.

Thus, this would also predict that when the network is damaged, then phonological errors both in comprehension and expression would occur as a consequence.

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In contrast to theories that postulate a single phonological lexicon for both input and output phonology,

some theories propose inadequate modality – specific representations, i.e, separate phonological input and output lexicons (Morton, 1970).

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Miclei etal, 1980, studied the relationship between expressive and receptive phonemic disorders in 69 aphasics.

They found no correlation between the degree of phonemic output disorder and the number of phonemic discrimination errors.

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Indian Studies on phonemic discrimination

Comprehension Deficits in Aphasics Dr. S. P. Goswami.

Doctoral Thesis Submitted to University of Mysore. Thesis No: 25.

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The aphasics scored poorer than normal subjects on the phonology section of LPT.

The normal subjects scored 47.83 (0.71) on phonemic discrimination, whereas,

The aphasics obtained mean score of 36.24 (SD – 14.20),

The mean and SD scores of various types of aphasics as follows:

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The performances of nominal and TMA were near normal.

Both these groups obtained a mean score of 47.30.

The responses of these aphasics were found to be immediate and accurate.

The TSM and Conduction aphasics exhibited similar type of performances in this section, with mean scores of 45.25 and 44.25 respectively.

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It was also noticed that the performance of TSA was better than conduction when the stimulus was presented verbally.

The responses of TSA were abundant with literal and verbal paraphasias.

The Broca’s aphasics obtained a mean score of 35.25.

Their performance was improved when the stimulus is presented in both verbally and graphically rather than verbal mode alone. 27

The Wernicke’s showed a mean of 37.43.

It was seen that the responses did not improve much, even when the stimuli were presented in both verbal and graphic modalities.

And the responses were dominated by paraphasias.

The global aphasics performed poorest performance in this section.

The few responses they made were just guesses.

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A WORKING MODEL OF SPEECH PRODUCTION AND SPEECH PERCEPTION (Blumstein 1994)

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The production of a word or words involves the selection of a word from the lexicon.

The encoding of the abstract phonological representation of a word in terms of the proper order of the segments and in terms of phonological context in which they appear.

And then the implementation of this phonetic string into a set of motor commands or motor programs to the vocal tract.

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Subsequent to the selection of a lexical word and the articulatory planning of the utterance,

the phonetic string is ultimately converted into a set of commands to the articulatory system.

It is seen that meaning requires the mapping from sound structure to lexical form.

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The auditory reception of words involves several potential transformations of the auditory input into a spectral representation based on

the extraction of more generalized auditory patterns or properties from the acoustic waveform

and the conversion of this spectral representation to a more abstract feature/ phonological representation and

ultimately the selection of a word from a set of potential words sharing phonological properties with the target word.

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Phonological and Semantic deficits arise at a different level of language processing,

and it is likely that the stage of processing at which the breakdown occurs, determines the influence on verbal communication.

Errors at the phoneme level seem to give more clues for the detection of the target word.

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In case of phonemic paraphasias, which result from an erroneous selection and/or sequencing of phonemes,

the phonological structure of the target word is partially available.

The target word is often recognizable.

Moreover, in the context of a pure disorder at the phoneme level self-corrections are also observed (e.g., Kohn & Smith, 1992).

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In severe conduction aphasia, phonological neologisms may arise, from which it is difficult to detect the target word (Hecaen et al., 1964).

In severe Wernicke’s aphasia, phonemic jargon is as incomprehensible as semantic jargon (Butterworth, 1985; Brown, 1981).

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Furthermore, a combination of semantic and phonological disorders may lead to a two-stage error: a semantic paraphasia in combination with a phonemic error, that makes the production of neologistic and unrecognizable words (Buckingham, 1981).

The phonological input and output routes are more generally agreed to be separable (Caramazza & Miceli, 1990; Howard, 1995; Romani, 1992).

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This view is supported by a large amount of case-reports of persons with selective disorders in the output route in the context of intact phonemic processing of auditory verbal material (Caplan & Waters, 1995; Kohn & Smith, 1995; Willshire & McCarthy, 1996).

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Phonological and phonetic deficits: Phonological and phonetic studies of aphasia

are evaluated with respect to issues of neural representation of speech and language.

The traditional dichotomy between posterior and anterior syndromes has been challenged in recent years.

In speech production, deficits at the phonological level are discussed in relation to psycholinguistic models of speech production, phonological features, underspecification, markedness, syllable structure, and sonority.

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Segmental deficits at the phonetic level are discussed primarily in relation to temporal parameters of consonants and vowels, segmental coarticulation, and speaking rate effects.

Production deficits are examined for phonemic stress, contrastive stress, lexical tones, tonal coarticulation, intonation, and foreign accent syndrome (FAS).

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Current psycholinguistic models of language production distinguish three major stages in the production of words and connected speech:

access, planning, and implementation.

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Deficits at Phonological Level Nearly all aphasic patients produce

phonological errors in their speech output.

All types of phonological errors can be found across diagnostic categories of aphasia.

Segmental error patterns reflect disruption at different stages of speech production that may be associated with different aphasic syndromes.

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Various psycholinguistic mechanisms have been hypothesized to account for phonemic paraphasias at stage – 2.

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1. Phonological features and underspecification theory:

Recent theories of generative phonology posit that features are organized in a hierarchical tree structure.

Blumstein in 1990 found that the majority of phoneme substitution errors reflect feature changes within a single tier rather than across tiers.

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Theories of underspecification have been proposed whose aim is to

explain when features may are absent in underlying or derived representations showed,

and how phonemic errors made by a conduction aphasic are related to syllabification processes that interact with underspecified segmental representations at different stages in phonological encoding.

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An analysis of phonemic paraphasias in French speaking aphasics supported the underspecified nature of coronal consonants.

Underspecification theory has also been applied to predict the location and quality of epenthetic vowels in phonemic paraphasias produced by French speaking aphasics (Beland, 1990).

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2. Markedness: It has been argued that markedness theory

can explain the pattern of phonemic paraphasias in aphasia.

Among other criteria, “marked” segments are considered to be more complex articulatorily and universally rather than “unmarked” segments.

Substitution errors of aphasic patients have been observed to involve replacement of marked segments with unmarked ones.

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The pattern of phonemic paraphasias was indistinguishable across clinical syndromes.

More recent work, however, has challenged the unitary treatment of different aphasic syndromes as well as the claim that markedness considerations play a critical role in accounting for the error patterns (Beland, 1990).

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3. Syllable Structure: Recent theories of phonology recognize the

syllable as a phonological constituent.

Phonemic substitution errors appear to be sensitive to syllable – internal hierarchical branching structure.

Few substitutions occur when the consonant is part of a consonant cluster.

The majority of consonant substitution errors occur when the consonant is preceded or followed by a vowel.

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These findings are inexplicable in a theoretical framework that treats the syllable as an unanalyzable whole.

Analyses of phonemic paraphasias across word boundaries show that the affected phonemes occur in like syllable positions.

Not all constituents of the syllable are equally prone to disruption.

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An analysis of jargon produced by two Wernicke’s aphasics revealed that the coda is more susceptible to impairment than the onset; nucleus is the most stable of the syllable – internal constituents (Stark & Stark, 1990).

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4. Sonority:

Sonority refers to the perceptual prominence of one phoneme relative to another.

Along a sonority scale, obstruents are considered to be the least sonorous, vowels the most sonorous.

The sonority sequencing principle holds that segments are optimally ordered so as to achieve a rise – fall sonority profile.

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An increase in sonority from the beginning of the syllable to the vowel peak followed by decrease in sonority from the vowel peak out to the end of the syllable.

Sonority sequencing principles have been invoked to explain phonological error patterns seen in fluent aphasia, especially in neologistic and jargon aphasia (Christman, 1994).

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Deficits at the Phonetic Level: The traditional view is that anterior aphasics

have a tendency to produce phonetic errors;

posterior aphasics have difficulty primarily at the phonological level.

The underlying cause of the phonetic errors has usually been attributed to a breakdown in articulatory implementation,

whereas phonemic errors have been described to a breakdown in access or planning the appropriate phonological output (Blumstien, 1990).

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The processes involved in the selection and planning of the sound structure of language seem to be broadly represented in the left dominant language hemisphere.

The implied basis for these errors is one of articulatory implementation, which are the commands to the articulators to encode the word are poorly timed and impaired.

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Studies of speech production in anterior aphasics have shown that these patients have difficulty producing phonetic dimensions that require the timing of two independent articulators.

These findings have emerged in the analysis of the production of two phonetic dimensions, voicing and nasality.

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i.e., voicing and nasality could indicate that these patients have an impairment that is affecting the articulatory implementation of particular phonetic features or alternatively,

the implementation of particularly articulatory maneuvers. (Blumstein, cooper, goodglass, stablender and glttlies, 1980)

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If patients have deficits related to the implementation of the feature voicing, they show impairments in the production of VOT as well as length preceding voiced and voiceless stop consonants.

Results indicated that although these patients show impairment in the implementation of the voicing phonetic dimension via VOT,

they are able to maintain the distinction between voiced and voiceless stops on the basis of the duration of the preceding vowel. (Baun, Blumstein, naeser and palumbo, 1990).

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Thus these patients do not have a disorder affecting the articulatory production of the feature voicing,

but a disorder affecting particularly articulatory maneuvers namely, the timing or integration of movements of two independent articulators.

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Analyses of the formant frequencies of spoken vowel utterances showed that

anterior aphasics including Broca’s aphasics maintain formant frequency characteristics of different vowels, despite increased variability in their productions (Kent an Rosenbeck 1983; Ryalls 1987).

Fricative durations do not differ significantly from those of normals (Harmes et al.1984).

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Investigations of coarticulation effects in anterior aphasics show that phonological planning is relatively intact,

but it is the ultimate timing or coordination of the implementation of the articulatory movements that is impaired. (Katz 1988; McNeil, 1988).

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1. Temporal parameters of Consonant and vowel production Acoustic, physiological and perceptual

investigations of consonant production deficits in aphasia support a dichotomy between phonological planning and phonetic implementation.

Anterior aphasics exhibit primarily deficits in articulatory implementation,

The consonant production deficits of posterior aphasics generally reflect problems of a phonological nature. 62

Anterior aphasics’ difficulties do not lie with particular phonetic features.

In anterior aphasics, voicing in initial stops and fricatives was impaired, whereas, vowel duration was relatively spared (Baum, 1996).

Cross linguistic comparisons have reinforced the notion that the phonological status of the durational attribute has little effect on speech production impairments of anterior aphasics.

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There is a marked compression of the VOT continuum regardless of the number of stop voicing categories that are present in the phonological system (Gandour, 1992).

Conversely, vowel duration at the syllable level appears to be relatively spared following brain damage regardless of whether it is used contrastively at the lexical level (Baum, 1990).

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Besides impairment in the timing of independent articulators,

anterior aphasics may have difficulties with the implementation of laryngeal gestures that closely interact with supralaryngeal vocal tract system (Blumstein, 1994).

Ryalls (1987) concluded that the degree of disturbance of vowel duration in aphasia varies depending on the size of the linguistic unit within which vowels are produced.

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Coarticulation The study of coarticulation provides

insights into the size of the planning units that can be programmed in the production of syllables and words as well as the dynamic aspects of speech production.

Acoustic, physiological and perceptual investigations of coarticulatory phenomena involving consonants and vowels present mixed findings on the issue of mechanisms underlying any coarticulatory deficits in brain – damaged patients. 66

Katz (1988) found no evidence of a deficit in anticipatory coarticulation in anterior and posterior aphasic English – speaking aphasics.

Anticipatory labial coarticulation was also found to be essentially intact in two German – speaking anterior aphasics.

Anticipatory coarticulation was found to be impaired in conduction aphasics.

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Speaking Rate effects:

Another interesting aspect of temporal control is the manipulation of speaking rate and its effects on segmental and suprasegmental production.

Although their changes in rate were of smaller magnitude than those for normal subjects, both anterior and posterior patients appear to be relatively unimpaired in their ability to manipulate speaking rate (Baum, 1996). 68

Yet temporal deficit patterns between speaking rate conditions are not same for anterior and posterior patients.

For example, vowel durations of nonfluent aphasics were not significantly different between slow and fast conditions.

In contrast, fluent aphasics, like normal subjects, produced shorter vowel durations at a faster speaking rate.

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Deficits in Speech Prosody Speech prosody can be used to signal

linguistic and emotional information.

A number of competing hypotheses have been proposed to account for the lateralization of linguistic prosody.

The ‘functional load’ hypothesis states that prosodic cues are processed differently in the left hemisphere depending upon whether they serve a linguistic or a nonlinguistic function. 70

A more restrictive version of hypothesis stipulates that the left hemisphere is specifically engaged for lexical contrasts (Packard, 1986).

The “parallel processing” hypothesis posits that both hemispheres may simultaneously participate in processing various components of the speech signal for which the hemisphere is specialized.

The left hemisphere has been hypothesized to mediate temporal information, the right hemisphere spectral information.

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Stress: Stress is an especially interesting for testing

hypothesis about hemispheric specialization of prosody because of its multiple acoustic correlates:

duration, amplitude, and F0.

An across the board deficit in all three acoustic correlates would imply a functional level disturbance at high level of linguistic representation.

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Selective deficits in any one or more of these multiple correlates, on the other hand,

would suggest that there may be differential lateralization for the processing of different prosodic parameters.

Acoustic investigations of LHD and RHD patients’ ability to produce lexical and phrasal stress contrasts have generally found a stress deficit in LHD patients only (Emmorey, et al, 1987).

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Instead of characterizing the deficit as a stress deficit,

LHD patients appear to have difficulty with the manipulation of durational cues, whereas,

the other acoustic correlates of stress remain relatively intact (Ouellette, 1994).

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It is possible that deficits in the processing of linguistic prosody attributed to LHD patients may be a secondary consequence of a more basic impairment in speech timing.

The stability of acoustic patterns in the speech of brain damaged patients depends primarily on the size of the temporal domain over which the linguistic unit is programmed.

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Intonation Contrary to the view that all aspects of

prosody are mediated by the RH, much of the acoustic phonetic evidence seems to indicate that intonation is more vulnerable to disruption in the speech of LHD than RHD patients.

Although the deficit is more severe in Broca’s aphasics, abnormalities in intonational patterns have also been observed in Wernicke’s aphasics.

Not all aspects of intonation are vulnerable to impairment. 76

The extent to which sentence declination patterns deviate from those of normals appears to depend largely on the size of the utterance.

Declination patterns were more likely to deteriorate in longer sentences.

A narrowing of the F0 range that has been observed in anterior LHD patients of nontonal languages does not generalize to tone languages.

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These crosslinguistic findings suggest that disturbances in F0 patterns in aphasic patients may be a secondary consequence of an underlying timing impairment.

The RH may be implicated in the control of global aspects of sentence intonation (Ryalls, 1988).

Baum & Pell (1997), however, found intonational characteristics to be spared in RHD patients as well as LHD patients, leading them to conclude that some aspect of intonation may be under control of subcortical structures.

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Gandour et al, (1995) similarly found certain aspects of intonation to be spared in LHD and RHD Thai – speaking patients.

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